1. Field of Use
This invention relates generally to shut-off and stop/check valves for fluids used in refrigeration systems or the like.
In particular, it relates to improved means for mounting a valve disc on a valve stem.
2. Description of the Prior Art
A manually operated shut-off valve typically comprises a hollow valve housing having a valve plate therewithin with a fluid passage therethrough and having a valve seat therearound. An externally threaded valve stem mounted for rotation and axial shifting movement in an internally threaded hollow valve stem sleeve operates a valve disc which is axially shiftable to open and close the fluid passage in response to rotation and axial shifting of the valve stem in the appropriate direction. Rotation of the valve stem causes the valve stem and the valve disc thereon to shift axially. Thus, the valve disc can move toward a seated position wherein it engages the valve seat (valve closed), or away from the valve seat to an unseated position wherein it is disengaged from the valve seat (valve open). In one type of valve, the valve disc is integral with the valve stem so that the valve disc rotates along with the rotating valve stem. Since the valve seat is stationary and the valve disc is rotatable relative thereto, friction and resultant wear occur at their interface during seating and unseating of the valve disc. Over time, such wear on either or both components can cause fluid leakage at the interface, even when the valve disc is fully seated and the valve is closed. In another type of valve, the valve disc is rotatably mounted on the valve stem and rotation or spinning of the disc is caused by the turbulent flow of the fluid through the valve. Valve disc rotation stops soon after the valve disc engages the valve seat as the valve closes and rotation does not resume until the valve disc is nearly disengaged from the valve seat. Such spinning causes excessive wear between the disc and valve stem. Both of the aforesaid types of valves often include babbitt metal inserts at the interface between the valve disc and valve seat. If the disc is allowed to spin on the stem when the valve is open, random mating of the disc and seat occurs upon closure. As a result the babbitt metal insert must be deformed differently to conform to the irregularities of the seat each time the valve is closed. This requires extra force to obtain a tight seat. Such insert is subject to mechanical wear and leakage and eventually needs to be replaced. Many attempts have been made to overcome these problems. For example, resilient washers made of rubber or plastic have been provided at the valve seat interface, such washers being mounted on either or both components. However, this arrangement is usually unsatisfactory in valves which handle high pressure fluids, or corrosive fluids, or abrasive fluids, because these fluids can damage or destroy rubber or plastic washers.
In so-called stop/check valves, as distinguished from conventional shut-off valves, not only must the valve disc move between open and closed positions in response to rotation and axially shifting of the valve stem, but the valve disc must also be capable of moving independently from open to closed position in response to pressure differentials on opposite sides of the valve disc which could cause unwanted reverse flow of fluid through the valve, even though the valve stem is still in an open position. When the valve operates as a check valve, the reverse flow pressure difference is usually low. Since this is the only force available to close the valve, it is not sufficient to obtain a tight seat with random mating. These requirements pose additional problems as regards the design, construction and operation of the valve disc mounting means in a shut-off and stop/check valve. Various prior art means have been proposed to prevent valve disc rotation in conventional shut-off valves but, very often, such prior art means are relatively complex in construction and mode of operation. Furthermore, such means are not well-adapted for application to stop/check valves.